While checking some info site I ran across a message re: charging e31 batteries. So after reading all the messages I conducted a test.

<With my limited experience with 8's, and my now 2 months of tracking/tracing electrical issues with the car I'm working on, I have now done both methods of attachments of a Battery Tender Plus.
First was to the obvious under hood posts, but the cord was constantly in the way, so I opted to move the Tender "bolt on" harness to the rear, in the trunk, since I was working there and both side panels were out.
I've just conducted a test, based on this post, and find that the batteries show same voltage.
I had installed the Tender bolt on harness on the left/drivers battery, with the ground wired bolted to the car ground post on the rear left side of the body.
(The manual says always disconnect the ground strap there first whenever disconnecting power)
Upon further inspection, I find that all "red power cables" are mounted to the rear right battery, and again after testing voltage on both batteries, they are still consistently the same.
Now please note: this is just my limited knowledge of this car and it power system.

In my experience with tenders, I find that there are two different types, one Battery Tender Plus 1.2 amp hour, which in my experience, does a good job of keeping batteries charged. ( I have 6 in different applications, cars, boats, and golf car/generator/lawn tractor batteries)
And another, called Optimizer ( marketed from Honda) which is .8 amp hour, but has a secondary function, what they call de-sulfate, where as it measure sulfation in the plates and spikes voltage for a programed time period to re-vitailze older batteries. It also has a light that indicates if that process has failed and the battery is No-Good.

In the resent past I have purchased two new Schumacher battery chargers, one 20 amp and the other 40 amp, they both have this (new to me) De-sulfation function.
With all my vehicles (toys), cars (SUV's), boats, Motorhome, golf car, generators etc, I'm constantly having to keep charged or charge my batteries. Some new and some not, so I'm inclined to make sure sulfation doesn't kill or reduce battery life.

Hope this is correct info...

regards>

Please let me know 'IF" I'm off base here. Batteries have become an important issue in all my successful recreation.

Wess,
In the 'old' days I used the "kill" switch (like you see on race cars; big red on/off switch) to save batteries not being used; I just put it 'in-line' between the solenoid and battery. Now, because of the computers and of course memory for the radio etc., one would not want to disconnect the battery power. I have used my 'trickle' charger for my boat (both engine and accessory) and car batteries, and never had a battery 'die'; as in being over charged or charged to many times. I really don't know about this "de-sulfation" (this I do know: as the battery de-charges the sulfate leaves the lead and as the battery is charged it reforms in the lead) of the battery but I do know if to much amps are being applied you can burn up a battery. My 'trickle' charger is a .5 amp and will stop charging when battery is 'charged' as well as not start charging until the battery gets below a "?" volts/amps.
I don't think I've really answered anything for you, just wanted to let you know...if you're using a good 'trickle' charger you should be okay.
P.Ford

Wess,
In the 'old' days I used the "kill" switch (like you see on race cars; big red on/off switch) to save batteries not being used; I just put it 'in-line' between the solenoid and battery. Now, because of the computers and of course memory for the radio etc., one would not want to disconnect the battery power. I have used my 'trickle' charger for my boat (both engine and accessory) and car batteries, and never had a battery 'die'; as in being over charged or charged to many times. I really don't know about this "de-sulfation" (this I do know: as the battery de-charges the sulfate leaves the lead and as the battery is charged it reforms in the lead) of the battery but I do know if to much amps are being applied you can burn up a battery. My 'trickle' charger is a .5 amp and will stop charging when battery is 'charged' as well as not start charging until the battery gets below a "?" volts/amps.
I don't think I've really answered anything for you, just wanted to let you know...if you're using a good 'trickle' charger you should be okay.
P.Ford

It's been a long process of chargers etc over the 30 some years of having toys etc.
Tenders as I refer to, are what some companies are calling them now, I know that Trickle chargers still exist and some old ones most likely.
So to my knowledge and what I have read on the the Del-Tron Battery Tender website about batteries....they explain the proper terminology & descriptions/operation for both.
We may be talking about the same type product.....just different name/identification....?

But the de-sulfation is supposedly the #1 problems and deteriorating factor for batteries according to what I'v read......of course this may also be marketing for the specific product.....but in my last trip to the battery distributor, he told me the same thing, if it sits without a charge and get low, and it's used or charged it takes a hard hit, get hot from the max amps it's getting, swell the cases, and thus reducing it's life.
My experience with my 11 coach batteries for my motorhome.

I've been provide with info on some devices that actualy de-sulfate batteries from the batteries own power source. High tech stuff that solar panel companies and users are quite aware of.....

So I'll keep researching the new info, and move my old chargers to the back of the shelf......or donate them.....

As far as the switch technic, I have a perko switch on my boat, that kills total power to everything.
But that's not possible like you mentioned for most of the new cars and equipment now-adays, too much memory for everthing, including seat location and mirrors.
I do also use a 100 amp switch to disconnect my (4) stereo batteries from the other (4) coach batteries, because the system can't handle the total load of 8, 550 amp hr batteries all at once. The converter really struggles, trying to put out 90 amps......
So once the coach batteries show good, I switch and charge the stereo batteries. The stereo batteries will last a few days with 4 amps drawing 30-40 amps peak.

that's enough trivial info.....thanx for sharing
wess

cut & paste....link....

http://batterytender.com/faqs.php/#1